Magnetic material



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June 2f4, 1930.

Patente-d. June 24, 1930 lUNITED `s'ra'rssl PATENT ori-lcs ausruw: ELMEN, or LEoNu, NEW JERSEY, AssIoNoB. 'ro WESTERN ELEc'rnIc comm, rNconPona'rED, or NEW YORK, N. Y., A Conom'rIoN or NEW You mGNE'rIc MATERIAL appumion mea 'naam-yl 1a,v semi 1ra-'160569.

This invention relates to magnetic materiale and electromagnetic systems. It has wide a plication and is especially useful where t e magnetizing forces are small, as in signaling systems.

Among the important characteristics of the material of this invention are high perme-Z ability, especially at low magnetizing forces, and high resistivity with consequent low eddy current losses.

This application is a continuation in par of application Serial No. 48,188, filed August 5, 1925.

Magnetic materials have been variously employed in electrical systems for such pur-` limited to relatively short cables for tele' phone purposes. Heretofore, the magnetic materials generally used for these purposes have been soft iron andsiliconsteel. The principal possible'rivals of iron are nickel and cobalt but they are far below iron in permeability atthe magnetizing forces involved in such apparatus. With nickel and cobalt, in this respect, stands Heuslers alloy of aluminum, manganese, and copper. It has been found that a composition of about nickel and 1A, copper, when tested at low magnetizing forces, gives a permeability higher than that of iron alone. It will be seen that with the exception. of aluminum, all these metals stand close together in their atomic weights and atomic numbers, andvin this specification lthe -ive {.lements, manganese, iron, cobalt, nickel ancopper, having the consecutive atomic numbers 25, 26,' 27, 28 and '29, will be referred to as constituting the magnetic group of felements.

'45 Recently,V alloys comprising elements of the magnetic group andlespecially those conl,sisting chiefly of nickel and iron, havebeen employedA to Agreat advantage,*particularly in connection with signaling systemsl and ap- 59 TPIuS in which the-magnetic kforces in- Magnetic materials have also been employed,

volved seldom exceed 0.2 gauss. Such alloys, and the method of pro'duc'ingvthemare dis-p` closed in UnitedStates Patent No. 1,586,884 granted to G. W. Elmen, June 1,1926, and 1n a plicants copending'application referred 55 y toaove.. y That applicati n discloses a composition comprising elements of thefsocalled mag'- netic group withthe additionlof axthird element and havinghigh permeability andre- 60 sistivity, and small hysteresis and eddy current losses. Among thev compositions mentionedis an alloy kof nickel, iron and silicon.

' The present invention relatesto magnetic alloys consistingfof at least two `elements'iof 65 the magnetic group `combined in suitable-proportions with silicon. -Thesea1loys,"w hen subjected to 'al vproper heat treatment and guarded against undue stresses and other dis- "turbing causes, not only develop andl retain;

an extremely high permeability at lowmagnetizing forcesof the order of 0.2 auss or l less, but at the same time have a. notaly high resistivity and consequent low eddy current loss. Furthermore, they can be applied with advantage to the continuous loading of signaling conductors in such a manner as to obtain the full benefit of the above 'noted desirable'properties. In its preferred present invention comprises nickel,l ironfand silicon properly proportioned and properly l heat treated as described in the following: detailed descriptionin connection with the drawing in which:` v .L

Fig; 1 shows graphically the relation v,between the resistivity kand the percentage of silicon in alloys comprisin nickel, -iron and silicon, the proportions o A nickel and v iron being approximately in the ratio of 78 to 22 90 Fig. 2 shows graphically the general trend of the initial permeabilityl withl respect to the?l percentage of silicon of the-same alloys; an I v l y Fig. 3 shows a signaling. conductor loaded 95 with the magnetic material `of this invention in the form of tape. n,

The curve of Fig. 1 shows that the resistivity of alloys containin as the basic vconstituents about 78% nic el aed. ..2. 2% iron 19 form the alloy off, the 870 -I fil may be increased by the addition of small amounts of silicon. The high resistivity of these alloys makes them particularly Well adapted for use Where loyv eddy current losses are desirable.

The curve of Fig. 2 shows the general trend of the initial permeability of this group of alloys with respect to the percentage of silicon. The samples upon which this curve is based were subjected tothe double heat treatment hereinafter desciibed. As shown by this curve, silicon iii percentages up to about 1% has little eil'ect on the initial permeability. ivhile larger quantities tend to decrease the initial permeability. The high resistivity together with the relatively high initial permeability of these alloys renders them better than iron for use as a loading material for signaling conductors, and for other uses Where the magnetizing forces are small and low eddy current losses are desirable, as in transformer and inductance coil cores.

The magnetization curves for this group of alloys generally folloiv the characteristics of the nickel-iron alloy containing TSf; nickel and 21T/3% iron as shoivn in application Serial No. 48,188 referred to above. The addition of silicon in increasing amounts causes the curve to rise less rapidly at the origin and reaclr a saturation point at a lower magnetizing force, although the effeet is not very marked for percentages of silicon below about 1%. For example, for a sample alloy containing about 0.51% silicon it was found that the strengths of magnetic fields for magnetizing forces of 0.05, 0.1, 0.2, 0.5, 1.0. 2.0, 5.0 and 10.0 gauss were 1,850, 5.680, 6,720, 8,540, 0,350, 9,800, 10,250 and 10,-100 gauss, respectively.

Although alloys of this group containing at least nickel and preferably about 78% nickel have been found to give the highest permeability and to be preferable for many purposes, these characteristics are not limited to these particular percentages of nickel, since, by decreasing the quantity of nickel in the material, alloys having a higher resistivity may be obtained, although the initial perm uibility of such alloys is ordinarily decreased by the use of smaller quantities of nickel. Any quantity of nickel in the alloy greater than Q5 to 30% which Will give a considerably higher initial permeability than iron may be employed in ironnickel-silicon compositions in accordance With this invention. F or many purposes in Which low eddy current loss is a prime requisite, as is the case for cores for loading coils and for loading material for signaling conductors, an alloy of a lower percentage of nickel, or a higher percentage of silicon, or both, may be found preferable to the alloys having higher initial permeability but ,lower resistivity.

In preparing magnetic materials according to this invention, nickel, iron and silicon in the desired proportions are fused together in an induction furnace and then poured into molds and formed or worked into the desired shape. For continuously loaded conductors a particularly suitable form for the alloy is that of a tape about 0.000 inch thick and about 0.125 inch in width.

In order to give the alloy the desired characteristics it is necessary to subject it to a process of heat treatment which will depend upon the composition of the alloy and upon the particular characteristics which it is desirable to produce in the material. An example of this heat treatment is the heating of the alloy to about 1100O C. and maintaining it at that temperature for a period 0l approximately one hour and subsequently cooling the material slowly. The rate of cooling and temperature to which the material is heated may be (letermined by experiment in cach case, in order that those characteristics sought in the particular material may be produced to the desired degree. An average rate of cooling which has been found to be suitable is approximately 5 C. per minute. rlhe temperature to which the material is heated may vary considerably from the above value. For materials containing higher percentages of silicon it may be desirable to heat the material to a somewhat higher temperature.

For alloys containing various ierceiitages of silicon it has in general been ound preferable to employ a modification of this heat treatment in which the alloy is reheated after the initial heat treatment, outlined above, to a temperature somewhat above its magnetic transition point. Vlhe material is then cooled to room temperature, past the magnetic transition point ata certain ate Which should be determined for each alloy, but which is preferably faster than that employed in an anneal, but not so fast as to set up strains in the material due to uneven cooling throughout the body.

A modified form of heat treatment which may be desirable in some instances is to omit the reheating process and cool the material from the original annealing temperature in two steps; cooling to a point slightly above the magnetic transition point being carried on at one rate, and from that point to room temperature at a more rapid rate.

lVhen the material is to be used for the continuous loading of signaling conductors, it is formed into a tape having substantially tlie dimensions stated above. This tape is produced by Working the alloy'into the form of a rod or bar by repeated steps of swaging and annealing. The bar is subsequent-ly drawn down to the form of a wire of about No. 20 B. & S. gauge and then passed between rollers whereby it is iiattened into tape of the propertliickness. This tape is then passed l about the central wire.

v(il) l conductor.

between cutting rolls or discs which trim its edges squarely at both sides and give the tape uniform width. n

The loaded conductor shown inv Fig. 8 con'i prises a stranded core consisting of a central cylindrical wire 11 enveloped by a plurality of surrounds 12 which are shaped to it +ogether closely to form a cylindrical annulus The magnetic material 13 in the form of tape is lWrapped helicall about the stranded core, as disclosed in U. Patent No. 1,586,887, granted to G. lV. Elmen, June y1, 1926.

When it is desired to use a loading material in the form of a wire rather than a tape the drawing processes as outlined above' are continued until the wire has the desired dimensions.

rAfter the loading tape has been applied to the core, it is given its final heat treatment by drawing the assembled loaded conductor through a furnace, for example of the type described in U. S. Patent No. 1,586,884 referred to above. This is an electric furnace of the muile type having a horizontal iron heating tube extending through the furnace and projecting a considerable distance beyond. The furnace is maintained at the optimum temperature for the particular composition of the alloy being employed. The length of the pass through 'the heating tube and the rate at which the conductor is moved are chosen so as to produce the most desirable magnetic characteristics in the loaded After cooling the conductor is insulated and formed into a cable in the usual manner.

It will be found that certain of these alloys are better suited for some particular uses than others, and that the characteristics of any alloy may be varied by the use of different heat treatments. No attempt has, therefore, been made to give an exhaustive analysis of the characteristics of each composition but merely to point out generally the characteristic advantages and uses of this group of alloys and some typical methods of producing the same, with the understanding and intention that other particular compositions and methods of production are comprised within the spirit and scope of the invention as described and claimed.

What is claimed is:

1. A magnetic material havin a higher permeability at low magnetizing forces than 'iron and comprising nickel, iron, and silicon as essential elements thereof, more than 25% of the nickel-iron content being nickel.

2. A magnetic material comprising no less than nickel and iron and silicon as essential elements thereof.

3. A magnetic material according to the preceding claim in which the silicon content Y is less than 1%.

Il. A magnetic material comprisngnickel,

silicon at least 25% of the iron-nickel con-v tent being nickel.

8. A loaded conductor comprising a conducting core, a layer of loading material wrapped helically thereabout, said loading material comprising nickel, iron and silicon.

as essential elements thereof, at least 70% of the nickel-iron content being nickel.

9. A magnetic material containing nickel and another element of the magnetic roup and heat treated to have higher permea ility at low-magnetizing forces than iron, said material including silicon in amounts suitable to increase the resistivity to a material extent as compared to a similar alloy from which silicon is omitted. l

10. An alloy comprising nickel, iron and silicon, heat treated to develop therein hi h permeability for magnetizing forces of t e order of 0.2 gauss and less, said alloy comprising 0.2% to 3% silicon, and of the remainder over 33% nickel and over 20% iron.

In. witness whereof, I hereunto subscribe my name this 11th day of January, A. D.

'GUSTAF W. ELMEN. 

